The present invention relates to a perpendicular magnetic recording medium and more particularly to a magnetic recording medium having an areal recording density greater than 23 gigabits per square centimeter.
Recently, an oxide granular medium using a material, in which an oxide is added to a CoCrPt-based alloy, has been proposed as a perpendicular magnetic recording medium having excellent thermal stability and a high media S/N value. For instance, a medium using CoCrPt—SiO2 as the magnetic recording medium is disclosed in IEEE Trans. Magn., vol. 38, p. 1976 (2002). As shown in IEEE Trans. Magn., vol. 36, p. 2396 (2000), a conventional CoCrPt medium with a Cr-segregated structure has a problem that the perpendicular uniaxial magnetic anisotropy energy is decreased due to the formation of an initial growth layer of the magnetic recording layer. The initial growth layer herein means an amorphous-like layer with a thickness of several nanometers. On the other hand, it is reported that the above-mentioned initial growth layer of the magnetic recording layer is not observed in an oxide granular medium as disclosed in JP-A No. 217107/2003. Moreover, as disclosed in the Abstracts of the 9th Joint MMM/INTERMAG Conference, BC-09, p. 84 (2004), it is reported that a 4 nm thick magnetic recording layer has almost the same perpendicular uniaxial magnetic anisotropy energy as a 15 nm thick layer, which means that an oxide granular medium gives a magnetic recording layer in which deterioration of the crystal structure can almost not be observed in the vicinity of the interface with the intermediate layer.